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Criteria for the Spectral Classification of B Stars in the Ultraviolet
Sonneborn, George; Rountree, Janet
A set of criteria for the classification of G stars from UV spectra alone, using standards drawn form the optical region, is developed. About 100 stars having normal MK spectral types in the range B0-B8, III-V, have been classified. The UV spectral types are found to be very consistent with the optical MK types, implying that it is possible to do …
First Results from the Goddard High-Resolution Spectrograph: Spectroscopic Determination of Stellar Parameters of Melnick 42, an O3f Star in the Large Magellanic Cloud
Butler, K.; Kudritzki, R. P.; Puls, J. +8 more
GHRS and optical (ESO 3.6 m) observations of the O3f star Melnick 42 in the 30 Doradus complex are reported. A first analysis reveals that with a luminosity of 2.3 x 10^6^ L_sun_ and a present mass of 100 M_sun_, Melnick 42 is one of the most luminous and massive stars known. An estimate of abundances indicates that iron and oxygen are very likely…
The Isolated Massive DA White Dwarf GD 50
Bergeron, P.; Wesemael, F.; Holberg, J. B. +3 more
Analysis of accurate hydrogen line profiles from optical and ultraviolet spectrophotometry shows that the hot DA white dwarf GD 50 (WD 0346-011) has an exceptionally high surface gravity of log g = 9.0 + or - 0.15; the derived parameters imply a mass of 1.2 solar mass and a radius of 0.0057 solar mass, if an interior composed of carbon and oxygen …
Persistence and Change in the Soft X-Ray Spectrum of the Quasar PG 1211+143
Elvis, Martin; Wilkes, Belinda J.; Giommi, P. +1 more
Two Einstein and three EXOSAT observations of PG 1211 + 143 over a 6 year baseline show that strong steep-spectrum low-energy X-ray emission is a persistent feature of this quasar. EXOSAT observations of PG 1211 + 143 detected a factor of 2.3 increase in its steep soft X-ray (C-band) flux in 18 days. The bulk of the soft X-ray emission of PG 1211 …
IUE Observations of NGC 5548, 1978--1988: The Sizes and Kinematics of the Broad-Line Region
Gaskell, C. M.; Koratkar, Anuradha P.
We have reextracted the IUE spectra of NGC 5548 taken between 1978 and 1988 and studied changes in the UV continuum flux and UV line intensities. We have used the cross-correlation method advocated by Gaskell & Sparke and refined by Gaskell & Peterson to investigate the structure and kinematics of the broadline region (BLR). We give an ext…
The Shape of the Ultraviolet Continuum of Quasars and Intergalactic Dust
Cheng, F. H.; Koratkar, Anuradha P.; Gaskell, C. Martin
We present measurements of the shape of the UV continuum of a large number of quasars. We investigate earlier claims that the near-UV spectral index α_UV_ gets flatter with increasing look-back time. We also investigate the dependence of α_UV_ on luminosity and radio type. The UV spectra of radio-quiet quasars are systematically slightly flatter t…
HST Observations of 3C 66B: A Double-stranded Optical Jet
Boksenberg, A.; Barbieri, C.; Weigelt, G. +17 more
The Faint Object Camera on the HST has imaged the central region of the synchrotron jet in 3C 66B with ultra-high spatial resolutions. The images have an angular resolution of 0.1'', corresponding to a linear scale of about 40 pc. This is a factor of more than 12 better linear resolution than previous optical images and more than 3 times better th…
The Ultraviolet Spectra of Nearby Radio Galaxies
Keel, William C.; Windhorst, Rogier A.
We report new and archival IUE SWP spectra for nine nearby radio galaxies (V < 15 mag), together with optical emission-line data for these galaxies as well as a number of candidates with weaker line emission. We examine both their UV line and continuum properties, as well as their UV and UV-optical line ratios. We find that: 1. Lyα emission is …
First Results from the Goddard High-Resolution Spectrograph: Evidence for Photospheric Microturbulence in Early O Stars: Are Surface Gravities Systematically Underestimated?
Heap, S. R.; Hubeny, I.; Altner, B.
GHRS spectra of two very hot stars provide evidence for the presence of microturbulence in their photospheres. In attempting to reproduce the observed spectra, theoretical models have been built in which the microturbulence is allowed to modify not only the Doppler line widths (classical 'spectroscopic' microturbulence), but also the turbulent pre…
The Ultraviolet Spectrum and Continuum Energy Distribution of the Bright Quasar H1821+643
Filippenko, Alexei V.; Halpern, Jules P.; Kolman, Michiel +1 more
We report on the first UV observations of the bright QSO H1821+643. With V = 14.2 mag and z = 0.297, H1821+643 is the second brightest object in the sky at z > 0.1. The IUE data are combined with new optical spectroscopy, and existing infrared and X-ray data, to reveal a strong optical/UV "big bump," which continues past the Lyman limit in the …